bsm actually doesn't work anymore, if you try Xime will ban you for 60 seconds
BSM isn't the only sprinting mod out there, in fact, it's one of the worst ones.
Also, nothing works 100% of the time.
As for my honest opinion on the subject:
I believe block-hitting has been nerfed (or heavily modified) along with hitboxes and other features related to PvP in 1.8+.
The wonderful part about this is making PvP overall more difficult, which includes making the hitboxes smaller, but it's a shame that block-hitting doesn't work properly.
PvP becomes more difficult when more aspects are involved.
Different strategies work great against different things, and if some of those things are removed, it takes the entire community a long time to adjust to it, and can even alter people's skill levels.
As for double-tapping, the extreme nerfing of that has made PvP much easier.
It took a required skill away from PvP, and basically gave everyone the chance to kill.
Remember how hard it was fighting those damn BSM users?
Well, guess what happened? Mojang decides: "Let's give everyone an unfair advantage!
"
Although that statement may seem ridiculous, it honestly is true. More experienced players have the advantage of strafing methods and other techniques, while new players have the advantage of keeping a sprint engaged for a long amount of time.
No wobble sprint for both parties, woo!
Mojang is not to blame, however, and neither is the community. Minecraft, although a major aspect of it is indeed PvP, we must consider that another large portion of the community enjoys playing survival, creative, or other gamemodes/minigames. Everything is everchanging in this game, which the creators committed to by releasing individual updates instead of entire new games for major updates.
In conclusion, I do believe that the sprint button has affected PvP, and I believe it has affected it in a negative way. Bad players are now less burdened to acquire an extra skill, and good players have to deal with them. That's just my opinion, however.
I'm going to go do my homework now.